1. Field of the Invention
The present invention relates to an optical waveguide device that utilizes the interaction of a guided optical wave with a magnetostatic wave.
2. Description of the Prior Art
The propagation of a magnetostatic wave (MSW) in a liquid phase epitaxial grown (LPE) film of an yttrium iron garnet (YIG) and the TM.revreaction.TE optical wave mode conversion, optical deflection, optical frequency shift or the like which is induced by the interaction of a guided optical wave with a magnetostatic wave in the film are reported, for example, in Journal of Applied Physics Vol. 50, No. 3 issued on March, 1979, PP. 2446 to 2448 and Applied Physics Letters 41(9), Nov. 1, 1982, PP. 779 to 781.
The optical waveguide device using the interaction between the magnetostatic wave and the guided optical wave can process a signal at high frequency as compared with an optical waveguide device that utilizes a surface acoustic wave. Also, the former optical waveguide device has such feature that it can be tuned depending on the magnetic field so that it is being noticed recently.
However, since specific Faraday rotation .theta..sub.F inherent in the YIG at the wavelength of 1.3 .mu.m is as small as 0.02 deg/.mu.m, this kind of device using the YIG presents, for example, relatively low TM.revreaction.TE optical wave mode conversion efficiency of about 4%, for example, with a 1.7 watt input microwave power.
Since as described above in the optical waveguide device using the interaction between the magnetostatic wave and the guided optical wave through the YIG, the specific Faraday rotation of the YIG is comparatively small, the efficiency, for example, mode conversion efficiency in the mode converter is low.
To solve the above-mentioned problem, it is proposed to make an optical waveguide device by using a bismuth-substituted-magnetic garnet in which yttrium Y is substituted by a large amount of bismuth Bi and of which the specific Faraday rotation .theta..sub.F at wavelength of, for example, 1.3 .mu.m is as high as 0.14 deg/.mu.m as compared with the YIG. However, even the optical waveguide device using the bismuth-substituted-magnetic garnet fails to realize this kind of device having satisfactory efficiency.